Ultrasensitive and label-free detection of prognostic and diagnostic biomarkers of sepsis on a AgNP-laden black phosphorous-based SERS platform

Abstract

Rapid and early detection of sepsis biomarkers is essential and an immediate need to prevent significant casualties of ICU patients caused by an uncontrolled infection in the patient's body. A highly sensitive and selective surface-enhanced Raman spectroscopy (SERS) based detection protocol has been established to detect the sepsis biomarkers. For this purpose, uniquely designed SERS substrate on black phosphorus (BP) flake are fabricated by a one-step and straightforward process where uniform silver nanoparticles (AgNPs) are synthesized over the BP surface, which in turn enhance the stability of BP flakes. Both the prognostic [interleukin-3 (IL-3)] and diagnostic [procalcitonin (PCT)] biomarkers are detected up to a limit of detection (LOD) as low as 1000 fM and 100 fM, respectively, where the SERS enhancement factor (EF) is obtained as high as in the order of ∼10¹⁴. A comprehensive study of Raman spectra has been carried out to explore the origin of observed Raman peaks of IL-3 and PCT, arising from various amino acids, which has never been reported earlier. The unknown signature Raman peaks for such biomarkers are identified at low energy regions, occurring due to structural variation of the two different protein chains even though both consist of the same possible amino acids. The findings of signature Raman modes of sepsis biomarkers help distinguish the Raman peaks of sepsis biomarkers in spiked clinical samples even in the simultaneous presence of both the biomarkers.